# std::isless

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< cpp‎ | numeric‎ | math

Defined in header `<cmath>` |  |
| (1) |
bool isless( float x, float y ); bool isless( double x, double y ); bool isless( long double x, long double y ); |  | (since C++11) (until C++23)
constexpr bool isless( /* floating-point-type */ x, /* floating-point-type */ y ); |  | (since C++23)
Additional overloads |  |
Defined in header `<cmath>` |  |
template< class Arithmetic1, class Arithmetic2 > bool isless( Arithmetic1 x, Arithmetic2 y ); | (A) | (since C++11) (constexpr since C++23)

1) Determines if the floating point number x is less than the floating-point number y, without setting floating-point exceptions. The library provides overloads for all cv-unqualified floating-point types as the type of the parameters x and y.(since C++23)
A) Additional overloads are provided for all other combinations of arithmetic types.

### Parameters

x, y | - | floating-point or integer values

### Return value

true if x < y, false otherwise.

### Notes

The built-in operator< for floating-point numbers may raise FE_INVALID if one or both of the arguments is NaN. This function is a "quiet" version of operator<.

The additional overloads are not required to be provided exactly as (A). They only need to be sufficient to ensure that for their first argument num1 and second argument num2:

If num1 or num2 has type long double, then std::isless(num1, num2) has the same effect as std::isless(static_cast<long double>(num1), static_cast<long double>(num2)). Otherwise, if num1 and/or num2 has type double or an integer type, then std::isless(num1, num2) has the same effect as std::isless(static_cast<double>(num1), static_cast<double>(num2)). Otherwise, if num1 or num2 has type float, then std::isless(num1, num2) has the same effect as std::isless(static_cast<float>(num1), static_cast<float>(num2)). | (until C++23)
If num1 and num2 have arithmetic types, then std::isless(num1, num2) has the same effect as std::isless(static_cast</*common-floating-point-type*/>(num1), static_cast</*common-floating-point-type*/>(num2)), where /*common-floating-point-type*/ is the floating-point type with the greatest floating-point conversion rank and greatest floating-point conversion subrank between the types of num1 and num2, arguments of integer type are considered to have the same floating-point conversion rank as double. If no such floating-point type with the greatest rank and subrank exists, then overload resolution does not result in a usable candidate from the overloads provided. | (since C++23)

### See also

less | function object implementing x < y (class template)
isgreater (C++11) | checks if the first floating-point argument is greater than the second (function)
C documentation for isless

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